Sewage and Our Rivers

January 12, 2023

A new way to understand storm overflows

Thames Water has recently created a publicly accessible web portal which publishes real-time information on when sewage treatment works within the Thames Water network are discharging raw (untreated) sewage to watercourses. This live map has brought the ongoing issue of sewage in our rivers back to public attention. The map can be accessed by anyone here. Although publication of such data will become a legal requirement in coming years, Thames Water’s launching of the portal ahead of it being mandated is a welcome step towards transparency around its operations. Due to the nature of how this data is collected, using Event Duration Monitoring (EDM) which measures start and end time of spills, volume and composition is not recorded and inaccuracies are not uncommon. You can read more about EDM and its limitations here. Despite these limitations, the live data does highlight the unacceptable scale of the problem of raw sewage discharge to watercourses.

Screenshot of the newly published live storm overflow map from Thames Water

Raw sewage spills occur particularly when rainfall infiltrates the sewage network, producing large volumes of dilute sewage, above the volumes that sewage treatment works (STWs) are designed to treat. Many STWs incorporate storage tanks which store excess inflowing raw sewage until it can be treated, thus reducing the extent to which the untreated sewage “spills” into watercourses. However, this is often inadequate to prevent spillage. There is an acceptance that some degree of spillage is inevitable (after heavy, intense rainfall). However, RTCT and many others believe raw sewage spills into rivers happen too often, and sometimes in circumstances where rainfall is less than extreme.

RTCT recognises that the contributory factors are complex. Thus, whilst we have concerns over STW capacity lagging behind demand from wastewater inputs, a key cause of raw sewage spillage is too much clean rain and groundwater making its way into the sewage network, and then on to STWs. Again, this is in part a consequence of a legacy of underinvestment in sewage networks (leaky sewage pipes enabling groundwater to infiltrate) but also increased urbanisation, resulting in more rain runoff going directly to the sewage network. Recognising the need to prevent problems caused by large volumes of clean water entering the sewage system, Thames Water recently published its Drainage and Surface Water Management Plan (DWMP). RTCT and the River Thame Catchment Partnership, which we co-host, welcome the DWMP approach, albeit we have concerns about the ambition and timescales of the DWMP in addressing the frequency and duration of raw sewage discharges from STWs.  The Catchment Partnership’s response to TW’s DWMP can be found here.

It’s not just spills

It’s worth distinguishing the issue of raw sewage spills from the overall performance of STWs under normal conditions – which is also a key issue of concern for RTCT. General poor water quality is a feature of the River Thame, with none of its tributaries attaining “good ecological status”. Whilst poor water quality is not solely caused by STWs, but also agricultural and urban runoff, monitoring and modelling led by UKCEH with RTCT shows a strong “signature” of sewage treatment effluent (treated) versus other sources. These results are supported by our growing body of evidence gathered by our new Water Quality Monitoring Network, an initiative where volunteers trained by RTCT are monitoring 40 strategically selected sites across the catchment every month. From anecdotes from concerned locals to citizen science data to rigorous scientific analysis, the evidence points to a chronic issue of unnaturally high nutrient levels in the catchment. And this issue isn’t new, pollution from sewage was a key driving factor behind the formation of RTCT and to this day we continue to push for change that will bring improvements to water quality & benefit wildlife and river users. We hope the accessible and visible nature of Thames Water storm overflow data will energise others to join our efforts to push for investment in sewage treatment capacity and improved infrastructure. We will continue our multi-faceted approach to advocating for tangible improvements.

What we’re doing to clean up the Thame

Engaging directly with Thames Water
  • Alerting Thames Water staff when sewage pollution issues are observed by our team or our network of volunteers – and seeking explanations
  • Contributing to all relevant consultations, like the 2025-2050 Drainage and Wastewater Management Plan – using the Thame Catchment Partnership as a basis for soliciting consultation input from a range of representative stakeholders
  • Seeking to influence investment in water infrastructure through the water company investment cycles, and staying abreast of progress in implementing investment plans
  • Advocating for the implementation of nature-based solutions that will not only improve water quality but also provide habitat benefits
Facilitating communication & collaboration to solve problems
  • Hosting the Thame Catchment Partnership, where Thames Water brings quarterly updates to a variety of stakeholders who may not otherwise have direct contact with them
  • Actively participating in the Thame Liaison Group (set up in 2014 by local campaigners after significant raw sewage spilling from Aylesbury STWs) which has improved the flow of information from Thames Water, management of the STW, and the environment along the Upper Thame valley
Increasing our understanding to build effective strategies for tackling pollution
  • Gathering and analysing water quality data across the catchment, including above and below sewage treatment works, to build our understanding of the issue and focus our efforts
Engaging and empowering the public to join our efforts
  • Encouraging the public to submit meaningful reports of pollution incidents to Thames Water at 0800 316 9800
  • Training and supervising citizen scientist volunteers across the catchment through our Water Quality Monitoring Network to collect valuable water quality samples to significantly expand the coverage of our data
  • Educating the public on the complex issues our rivers face and how they can help

What can you do to help?

  • If you live in the River Thame catchment, we encourage you to register as a River Thame Conservation Trust volunteer to get involved with the variety of opportunities we offer to help protect and restore rivers.
  • Keep up-to-date with our work by following us on Twitter & Facebook and signing up for our quarterly newsletter.
  • If you see what you think is a pollution event (which can come from a range of sources, not just STWs) call the Environment Agency on 0800 80 70 60 and Thames Water on 0800 316 9800. Make your observations count by always recording and submitting the following:
  • Record the exact date and time of your observation.
  • Record the exact location. Use What3Words or Grid Reference Finder to make your location as accurate as possible.
  • Take photos and write down exactly what you’re observing (Sewage solids? Toilet debris? Soap-suds or a milky-looking discharge? Grey coloured water? Noticeable sewage or strong chemical smells?)
  • Attempt to locate the exact point of discharge if possible, like a running pipe. Be mindful that the source may be underwater, stay safe and do not enter watercourses that appear to be polluted with raw sewage or are in a state of flood.
  • When making a report to the Environment Agency, ask for the number assigned to your report. If the situation persists, make a follow-up call and give this report number.

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